Stavros Dimas, Europe's ebullient environment commissioner, is in no doubt that the proposals on climate and energy just unveiled by the European Commission are a major contribution to curbing greenhouse gas emissions.

The Commission is proposing that Europe call for and negotiate for a 30% cut in greenhouse gas emissions by all developed nations by 2020.

Whether those negotiations are successful or not, it wants the 27 EU states to adopt a legally-binding unilateral target of at least 20%.

"This is not a step forward, but a leap forward to a low carbon world," he enthused to reporters at a Brussels news briefing.

"This is the first time that any country or region has come forward with such a unilateral target."

And he is right. The UK's target of 60% cuts by 2050, the 75% figure floated by French President Jacques Chirac, Arnold Schwarzenegger's 80% ambition, are all as yet just aspirations.

Even if any of these targets became legally binding, how should a country or US state deal with itself if it fails?

Close up

The Commission's proposal is interesting for two main reasons. Firstly, the target date of 2020 is close enough that concrete measures and concrete progress are clearly required on a timescale of several years, so it is possible to measure action against rhetoric in a meaningful way.

I think it's an important signal and very courageous

Yvo de Boer, UNFCCC

The second aspect is that given the way the European Union works, the Commission could be given the powers to act as referee and levy sanctions on states which fail to meet their targets.

The Commission aims not only to reduce Europe's emissions, but to break the paralysis which has struck United Nations climate negotiations in recent years.

"I think it's an important signal and very courageous what the Commission is proposing," said Yvo de Boer, Executive Secretary of the UN climate change convention (UNFCCC).

"What you see in negotiations is everybody waiting for everybody else to make the first move," he told the BBC News website.

"Now the Commission has made the first move and indicated it's willing to go further, and I hope that will enable us to deal with the current logjam."

Happy landings?

Environmental groups have given the proposals a mixed reception. Some maintain that the 20% unilateral figure is too low; others are more appreciative.

Stronger action on the car industry is necessary; it's time for the stick to come out of the closet

Hans Verolme, WWF

"I think we would like to see a stronger package which is more specific in places," said Hans Verolme, director of WWF's global climate campaign, "but overall this is an interesting proposal.

"We would urge governments to look at it closely and not to weaken it."

And that, of course, is the biggest caveat; so far, the Commission's proposals are just that, and there is plenty of scope for weakening them. They do not even amount yet to a formal draft of legislation.

So there are many obstacles ahead before Mr Dimas can be sure his leap forward is going to land in a celebratory cake, rather than something equally soft and rather less pleasant.

Self-interest will inevitably raise its head, with some business groups arguing that unilateral cuts of this magnitude will bring economic deprivation in competition with the US and Japan.

European governments are likely to be split on the idea. The 20% figure fits in with the UK's vision, and is likely to be well received in capitals such as Stockholm and Berlin where greenhouse gas reductions have already been achieved.

But countries which are way off achieving their current Kyoto Protocol targets, such as Spain and Austria, may well lobby against a new round.

Here, the European Commission has clearly scored heavily by combining the interests of its environment and energy operations. It has been a matter of intense frustration for some environment thinkers that in most governments, the two issues are dealt with separately when one depends so intimately on the other.

It wants clear targets for renewable energy and energy efficiency, again of 20% by 2020. The use of the term "primary energy" rather than "electricity" for renewables is very interesting, as it bundles up heat and power generation in one bag.

Given the differing political views across Europe on nuclear fission, the Commission was hardly likely to come down firmly for or against it.

And yet nuclear, which accounts for about 30% of the continent's electricity, is arguably the obvious way to switch large swathes of generation away from fossil fuels at a stroke.

It is clear that the Emissions Trading Scheme (ETS), the EU's principal mechanism for bringing emissions down, will be enhanced beyond 2012.

But the ETS deals principally with large-scale emitters, the power stations, industrial energy suppliers and cement manufacturers. True, aviation is being included; but road transport is unaffected, as are some domestic sources of emissions.

The Commission has neatly dodged the difficult nuclear question

As yet there is no mechanism for addressing this. A scheme under which car manufacturers vowed to improve the efficiency of their vehicles has not brought about meaningful change, the Commission believes, and mandatory targets are an option.

"Stronger action on the car industry is necessary; the voluntary agreement was a carrot and stick arrangement, and it's now time for the stick to come out of the closet," said Mr Verolme.

"But what kind of agreement can be reached I'm not sure; with the car industry being global, it's not a simple package to put together."

And even improving vehicle efficiency will not reduce emissions if vehicle use continues to grow.

Biofuels are the other approach for road transport. The Commission is proposing a legally-binding target of sourcing 10% of road fuels from plants by 2020; but that still leaves 90% coming from traditional petrol or diesel.

The European Commission has put an important toe into steadily warming waters with its package of proposals. But large sections of the water are still cloudy; and the swimmer has yet to leave the shore.